Lexus has introduced the next generation of its trend-setting RX luxury utility vehicles for 2010, the V6-powered RX 350 and the hybrid RX 450h. Lexus inaugurated the luxury crossover category with the original RX 300 model in 1998 and introduced the first-ever luxury hybrid in 2005. More than one million Lexus RX models have been sold worldwide, making it the most successful luxury utility vehicle. The new RX350, which reaches Lexus showrooms in February 2009 with the RX450h hybrid a few months later, once again raises the bar for design, engineering and luxury innovation in the segment.
Engine/Transmission/Drivetrain/Performance
The 2010 Lexus RX 350 teams a revised 3.5-liter V6 engine with an all-new six-speed Multi-Mode Automatic Transmission. New intake and exhaust manifolds improve engine breathing for enhanced performance and fuel economy. Horsepower is increased to 275 at 6,200 rpm from 270, while Lexus maximized the torque output to better meet the needs of luxury crossover drivers. Ninety percent or more of the 256 lb.-ft. of peak torque is available from 2,300 to 6,100 rpm, an optimal range where torque is most utilized. An insulated engine cover, styled in the shape of two cylinder banks, conceals the new V6 to help ensure a quiet cabin; easy-access points facilitate routine service.
Dual Variable Valve Timing with intelligence (VVT-i) is used to control both intake and exhaust camshafts independently, optimizing engine performance at all speeds and loads. Refinements to the valvetrain, including roller rocker arms and slimmer valve stems, reduce friction and weight to improve fuel economy. Also helping to enhance torque is the improved Acoustic Control Induction System (ACIS), which varies the intake runner length in response to engine speed and throttle position. The ETCS-i (Electronic Throttle Control System-intelligent) softens throttle response during initial acceleration for smoother takeoff and to help reduce wheel spin.
The 2010 RX 350’s new six-speed automatic transmission replaces the previous five-speed. Using miniature high-flow linear solenoids to control transmission-fluid line-pressure, the transmission yields quicker shifting response. The torque converter uses a new low-speed lockup damper to enable lock-up from second to sixth gear to help improve the fuel economy.
When applying the accelerator pedal rapidly during kick-down, the new direct-downshift control allows the transmission to directly shift from sixth to third or fifth to second, skipping the intermediate gears to achieve the quickest response. Under normal kick-down pedal application, downshift control uses the intermediate gears to ensure the smoothest shift is attained. “Shift shock,” which was already commendably low in the previous model’s five-speed transmission, is further reduced.The Multi-Mode Automatic Transmission allows the driver to shift manually when desired by first moving the gated shift lever to the “S” slot and then pushing it forward ("+") to up shift and backward ("-") to downshift. An Artificial Intelligence shifting (AI-SHIFT) control, new to RX, sets shift patterns based on the vehicle speed and throttle position and estimates road conditions and driver input to automatically control the shift pattern. For example, when driving in hilly areas, AI-SHIFT can prevent unnecessary shifting. When descending inclines, the transmission prevents up shifts to achieve more engine braking.
All-Wheel Drive
Lexus again offers its RX 350 and RX 450h crossover models with a choice between front-wheel drive and all-wheel drive. The RX 350 introduces an all-new electronically controlled Active Torque Control AWD system. As in the previous RX 400h, the RX 450h hybrid uses a separate rear electric motor-generator to provide power to the rear wheels when road conditions or throttle response dictates.
The previous RX 350 model’s AWD system used a viscous coupling locking center differential to provide 50:50 torque distribution. In the 2010 RX 350, Active Torque Control AWD uses an electronically controlled coupling ahead of the rear differential to vary torque distribution anywhere from 100:0 to 50:50 front to rear, depending on driving dynamics and road conditions. The new AWD system is 35 lbs. lighter than the previous system and reduces parasitic losses by 30 percent.
When accelerating, or starting off on a low-grip surface, torque is quickly provided to all four wheels. At steady speeds, torque is sent only to the front wheels, enhancing fuel efficiency.
For handling agility and control, the AWD system increases rear-wheel torque when the vehicle’s front tires start to lose traction and decreases rear-wheel torque when the vehicle’s rear tires start to lose traction. On rough or sandy terrain, an AWD LOCK switch provides enhanced traction performance for low-speed maneuvering (if in LOCK mode, the system reverts to AUTO mode when speed exceeds 25 mph). To help prevent a tight corner-braking condition (shuddering) during low-speed cornering, the system reduces rear wheel torque.
Hybrid Powertrain
The 2010 RX 450h introduces an updated version of Lexus Hybrid Drive, featuring a 3.5-liter V6 Atkinson-cycle engine, lighter electric motors, a smaller and lighter power-control unit and other fuel-saving innovations. It offers up performance similar to V8s with better combined fuel economy than the average four-cylinder mid-size sedan. With an EPA-estimated[1] 28 mpg city and 27 mph highway (26 mpg for the AWD), it earns 8-12 percent better fuel economy than its acclaimed predecessor. All this while producing 295 total system horsepower, which is 27 more than the current generation RX400h.
A full hybrid, the RX 450h can operate in electric-only or gas-engine-only modes as well as a mode that combines the power of both. Extended electric-mode operation during low-speed or stop-and-go driving conditions helps reduce fuel consumption. Under certain circumstances, a new driver-selectable EV mode can allow the vehicle to be driven short distances using only the electric motors.
The RX 450h will achieve Super Ultra Low Emission Vehicle (SULEV) certification in California (Tier 2-Bin 3 in other states), producing nearly 70 percent fewer smog-forming emissions than conventionally powered vehicles.
With the Atkinson cycle, the gasoline engine’s intake valves are closed late to delay beginning of compression, resulting in a higher expansion ratio. That reduces intake and exhaust energy losses for more efficient combustion and improved fuel economy. The gas engine alone produces 245 horsepower at 6,000 rpm, up from 208 in the previous RX 400h; torque is 234 lb.-ft. at 4,800 rpm as compared to 212 at 4,400 rpm from the previous RX 400h’s 3.3-liter V6. The Atkinson cycle also reduces exhaust temperature. A new cooled Exhaust Gas Recirculation (EGR) system reduces it further still, helping economy by eliminating the fuel enrichment otherwise needed to help prevent catalyst overheating under high loads.
A 288V DC Nickel Metal Hydride (Ni-MH) battery pack fits neatly under the rear seat and is more compact and lighter than in the previous model. A boost converter efficiently raises voltage to 650V DC, and an inverter changes this to 650V AC for the front-mounted 123-kW electric motor-generator. The boost converter and inverter are enclosed in the power-control unit, which also houses the condenser. The new power-control unit is 17.6 lbs. lighter than the previous unit and about 40 percent smaller. Losses have been reduced by more than 10 percent, enhancing fuel economy.
The RX 450h front-wheel-drive model’s hybrid powertrain employs two motor-generators: MG1, the engine-driven generator, is a starter and can charge the battery pack or power other electric motors as needed; MG2 is the front-drive motor. Power from the gas engine and MG2 is distributed to the drive wheels via a planetary gear-type continuously variable transmission. MG1 controls the output speed of the transaxle through the planetary gear set, without clutches or a viscous coupling. MG2 delivers similar maximum torque as in the previous model, but over a wider range for better response and smoother performance. When the RX 450h is coasting or braking, the electric motors function as generators, capturing energy that would normally be lost as heat through the brakes and transforming it into electricity to recharge the batteries.
The all-wheel-drive RX 450h adds a third, rear-mounted motor-generator (MGR) to drive the rear wheels, eliminating the need for power-transfer gearing or a driveshaft from the front. The hybrid system electronically varies front and rear torque distribution depending on traction conditions.
A new two-step flywheel damper absorbs small torque fluctuations and also the minor vibration produced when the gasoline engine starts and stops. A SNOW mode slows accelerator-pedal response to help reduce the possibility of wheel spin.
Multi-Mode, a feature adapted to the vehicle’s electronically controlled continuously variable transmission, allows the driver to control engine braking for enhanced maneuverability on rough or winding roads. The AI-SHIFT feature, adopted on a hybrid for the first time, selects and holds the optimal range when driving downhill or on inclines, providing a smoother driving experience.
The power-steering pump, water pump and air-conditioning compressor are driven electrically rather than by the engine, reducing parasitic losses.
To enhance fuel economy, a new exhaust heat-recovery system circulates engine coolant through a unit installed in the exhaust pipe behind the catalytic converter. This new feature reduces engine warm-up time, allowing it to stop earlier, more often, and for longer periods, improving both fuel economy and emissions.
Active Safety
The Vehicle Dynamics Integrated Management (VDIM) handling technology is now available on the RX 350 and remains standard on the RX 450h. The VDIM system anticipates loss of vehicle control in virtually any direction. VDIM governs all of the vehicle’s dynamic handling systems – the Anti-lock Braking System (ABS), Brake Assist, Vehicle Stability Control (VSC) and Traction Control (TRAC) – employing them collectively and seamlessly to make corrections while allowing higher dynamic capability. VDIM also interfaces with the electronic throttle control system.
The system’s enhanced VSC function adds steering assist torque to help aid handling on a split-friction surface. The VDIM system also provides a limited slip differential effect. The TRAC and VSC functions can also be switched off, for example, when the driver needs to free the vehicle when stuck in mud or snow.
The new RX adopts Hill-start Assist Control, which uses brake pressure to help prevent the vehicle from moving backward when starting out on an incline. This system does not wait to detect rollback, however. It can be controlled by the driver and works in both forward and reverse. While the vehicle is stopped and the brake pedal is depressed, pushing it further activates the feature. Brake pressure is then maintained for approximately two seconds after the brake pedal is released and the driver switches to the accelerator pedal.
The previous generation RX offered Lexus’ Adaptive Front-lighting System (AFS), which guided headlamps into a turn. The 2010 RX models introduce the new Intelligent AFS, which for the first time on a Lexus is being used for high beams of the HID headlamp equipped models, and for the low beams of the LED equipped RX 450h models. When entering a corner, AFS estimates where the vehicle will be in three seconds, based on the vehicle speed and the angle of the tires, and adjusts the lateral aim of the headlamps. AFS can be switched off by the driver if desired. AFS also includes an auto-leveling function.
Using a camera mounted on the inner rear view mirror, a new available automatic high beam system switches between high and low beams in response to oncoming vehicles and those traveling in front, or when other ambient sources are detected, helping reduce driver inconvenience.
The optional Pre-Collision System (PCS) with Dynamic Radar Cruise Control uses millimeter-wave radar to measure and maintain a pre-set following distance from a vehicle traveling ahead. The radar sensor can detect certain obstacles in front of the car, and a PCS computer with vehicle speed, steering angle and yaw-rate inputs helps to determine whether a collision is highly possible. In such a situation, PCS preemptively retracts front seat belts and pre-initializes Brake Assist so that increased braking will be applied the instant the driver depresses the pedal.
